TeX mode¶

TeX-compatible output is produced when the -t option is specified. You must use a TeX driver that supports tpic version 2 specials. (tpic was a fork of AT&T pic by Tim Morgan of the University of California at Irvine that diverged from its source around 1984. It is best known today for lending its name to a group of \special commands it produced for TeX.)

Lines beginning with \ are passed through transparently; a % is added to the end of the line to avoid unwanted spaces. You can safely use this feature to change fonts or the value of \baselineskip. Anything else may well produce undesirable results; use at your own risk. By default, lines beginning with a dot are not treated specially—but see the -c option.

In TeX mode, pic will define a vbox called \graph for each picture. Use GNU pic's figname command to change the name of the vbox. You must print that vbox yourself using the command

\centerline{\box\graph}

\centerline{\raise 1em\box\graph}

\def\gpicbox#1{%


  \vbox{\unvbox\csname #1\endcsname\kern 0pt}}

Commands¶

Several commands new to GNU pic accept delimiters, shown in their synopses as braces { }. Nesting of braces is supported. Any other characters (except a space, tab, or newline) may be used as alternative delimiters, in which case the members of a given pair must be identical. Strings are recognized within delimiters of either kind; they may contain the delimiter character or unbalanced braces.

for variable = expr1 to expr2 [by [*]expr3] do X body X

Set variable to expr1. While the value of variable is less than or equal to expr2, do body and increment variable by expr3; if by is not given, increment variable by 1. If expr3 is prefixed by * then variable will instead be multiplied by expr3. The value of expr3 can be negative for the additive case; variable is then tested whether it is greater than or equal to expr2. For the multiplicative case, expr3 must be greater than zero. If the constraints aren't met, the loop isn't executed. X can be any character not occurring in body.

if expr then X if-true X [else Y if-false Y]

Evaluate expr; if it is non-zero then do if-true, otherwise do if-false. X can be any character not occurring in if-true. Y can be any character not occurring in if-false.

print arg ...

Concatenate and write arguments to the standard error stream followed by a newline. Each arg must be an expression, a position, or text. This is useful for debugging.

command arg ...

.PS
x = 14
command ".ds string x is " x "."
.PE
\*[string]

x is 14.

sh X command X

Pass command to a shell.

copy "filename"

Include filename at this point in the file.

copy ["filename"] thru X body X [until "word"]

copy ["filename"] thru macro [until "word"]

.PS
copy thru % circle at ($1,$2) % until "END"
1 2
3 4
5 6
END
box
.PE

.PS
circle at (1,2)
circle at (3,4)
circle at (5,6)
box
.PE

reset

reset pvar1[,] pvar2 ...

Reset predefined variables pvar1, pvar2 ... to their default values; if no arguments are given, reset all predefined variables to their default values. Variable names may be separated by commas, spaces, or both. Assigning a value to scale also causes all predefined variables that control dimensions to be reset to their default values times the new value of scale.

plot expr ["text"]

This is a text object which is constructed by using text as a format string for sprintf with an argument of expr. If text is omitted a format string of "%g" is used. Attributes can be specified in the same way as for a normal text object. Be very careful that you specify an appropriate format string; pic does only very limited checking of the string. This is deprecated in favour of sprintf.

var := expr

.PS
x = 3
y = 3
[
x := 5
y = 5
]
print x   y
.PE

5 3

Expressions¶

The syntax for expressions has been significantly extended.

x ^ y (exponentiation)
sin(x)
cos(x)
atan2(y, x)
log(x) (base 10)
exp(x) (base 10, i.e. 10^x)
sqrt(x)
int(x)
rand() (return a random number between 0 and 1)
rand(x) (return a random number between 1 and x; deprecated)
srand(x) (set the random number seed)
max(e1, e2)
min(e1, e2)
!e
e1 && e2
e1 || e2
e1 == e2
e1 != e2
e1 >= e2
e1 > e2
e1 <= e2
e1 < e2
"str1" == "str2"
"str1" != "str2"

String comparison expressions must be parenthesised in some contexts to avoid ambiguity.

Other changes¶

A bare expression, expr, is acceptable as an attribute; it is equivalent to dir expr, where dir is the current direction. For example

means draw a line 2 inches long in the current direction. The ‘i’ (or ‘I’) character is ignored; to use another measurement unit, set the scale variable to an appropriate value.

The maximum width and height of the picture are taken from the variables maxpswid and maxpsht. Initially, these have values 8.5 and 11.

Scientific notation is allowed for numbers. For example

Text attributes can be compounded. For example,

is valid.

There is no limit to the depth to which blocks can be examined. For example,

[A: [B: [C: box ]]] with .A.B.C.sw at 1,2
circle at last [].A.B.C

is acceptable.

Arcs now have compass points determined by the circle of which the arc is a part.

Circles, ellipses, and arcs can be dotted or dashed. In TeX mode splines can be dotted or dashed also.

Boxes can have rounded corners. The rad attribute specifies the radius of the quarter-circles at each corner. If no rad or diam attribute is given, a radius of boxrad is used. Initially, boxrad has a value of 0. A box with rounded corners can be dotted or dashed.

Boxes can have slanted sides. This effectively changes the shape of a box from a rectangle to an arbitrary parallelogram. The xslanted and yslanted attributes specify the x and y offset of the box's upper right corner from its default position.

The .PS line can have a second argument specifying a maximum height for the picture. If the width of zero is specified the width will be ignored in computing the scaling factor for the picture. GNU pic will always scale a picture by the same amount vertically as well as horizontally. This is different from DWB 2.0 pic which may scale a picture by a different amount vertically than horizontally if a height is specified.

Each text object has an invisible box associated with it. The compass points of a text object are determined by this box. The implicit motion associated with the object is also determined by this box. The dimensions of this box are taken from the width and height attributes; if the width attribute is not supplied then the width will be taken to be textwid; if the height attribute is not supplied then the height will be taken to be the number of text strings associated with the object times textht. Initially, textwid and textht have a value of 0.

In (almost all) places where a quoted text string can be used, an expression of the form

sprintf("format", arg, ...)

can also be used; this will produce the arguments formatted according to format, which should be a string as described in printf(3) appropriate for the number of arguments supplied. Only the modifiers “#”, “-”, “+”, and “ ” [space]), a minimum field width, an optional precision, and the conversion specifiers %e, %E, %f, %g, %G, and %% are supported.

The thickness of the lines used to draw objects is controlled by the linethick variable. This gives the thickness of lines in points. A negative value means use the default thickness: in TeX output mode, this means use a thickness of 8 milliinches; in TeX output mode with the -c option, this means use the line thickness specified by .ps lines; in troff output mode, this means use a thickness proportional to the pointsize. A zero value means draw the thinnest possible line supported by the output device. Initially, it has a value of -1. There is also a thick[ness] attribute. For example,

would draw a circle using a line with a thickness of 1.5 points. The thickness of lines is not affected by the value of the scale variable, nor by the width or height given in the .PS line.

Boxes (including boxes with rounded corners or slanted sides), circles and ellipses can be filled by giving them an attribute of fill[ed]. This takes an optional argument of an expression with a value between 0 and 1; 0 will fill it with white, 1 with black, values in between with a proportionally gray shade. A value greater than 1 can also be used: this means fill with the shade of gray that is currently being used for text and lines. Normally this will be black, but output devices may provide a mechanism for changing this. Without an argument, then the value of the variable fillval will be used. Initially, this has a value of 0.5. The invisible attribute does not affect the filling of objects. Any text associated with a filled object will be added after the object has been filled, so that the text will not be obscured by the filling.

Additional modifiers are available to draw colored objects: outline[d] sets the color of the outline, shaded the fill color, and colo[u]r[ed] sets both. All expect a subsequent string argument specifying the color.

circle shaded "green" outline "black"

To change the name of the vbox in TeX mode, set the pseudo-variable figname (which is actually a specially parsed command) within a picture. Example:

The picture is then available in the box \foobar.

pic assumes that at the beginning of a picture both glyph and fill color are set to the default value.

Arrow heads will be drawn as solid triangles if the variable arrowhead is non-zero and either TeX mode is enabled or the -n option has not been given. Initially, arrowhead has a value of 1. Solid arrow heads are always filled with the current outline color.

The troff output of pic is device-independent. The -T option is therefore redundant. All numbers are taken to be in inches; numbers are never interpreted to be in troff machine units.

Objects can have an aligned attribute. This will only work if the postprocessor is grops(1) or gropdf(1). Any text associated with an object having the aligned attribute will be rotated about the center of the object so that it is aligned in the direction from the start point to the end point of the object. This attribute will have no effect on objects whose start and end points are coincident.

In places where nth is allowed, 'expr'th is also allowed. “'th“ is a single token: no space is allowed between the apostrophe and the “th”. For example,

for i = 1 to 4 do {


   line from 'i'th box.nw to 'i+1'th box.se
}